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.TH VPRINTF 3C "February 21, 2023"
.SH NAME
vprintf, vfprintf, vsprintf, vsnprintf, vasprintf \- print formatted output of
a variable argument list
.SH SYNOPSIS
.nf
#include <stdio.h>
#include <stdarg.h>

\fBint\fR \fBvprintf\fR(\fBconst char *\fR\fIformat\fR, \fBva_list\fR \fIap\fR);
.fi

.LP
.nf
\fBint\fR \fBvfprintf\fR(\fBFILE *\fR\fIstream\fR, \fBconst char *\fR\fIformat\fR, \fBva_list\fR \fIap\fR);
.fi

.LP
.nf
\fBint\fR \fBvsprintf\fR(\fBchar *\fR\fIs\fR, \fBconst char *\fR\fIformat\fR, \fBva_list\fR \fIap\fR);
.fi

.LP
.nf
\fBint\fR \fBvsnprintf\fR(\fBchar *\fR\fIs\fR, \fBsize_t\fR \fIn\fR, \fBconst char *\fR\fIformat\fR, \fBva_list\fR \fIap\fR);
.fi

.LP
.nf
\fBint\fR \fBvasprintf\fR(\fBchar **\fR\fIret\fR, \fBconst char *\fR\fIformat\fR, \fBva_list\fR \fIap\fR);
.fi

.SH DESCRIPTION
The \fBvprintf()\fR, \fBvfprintf()\fR, \fBvsprintf()\fR, \fBvsnprintf()\fR, and
\fBvasprintf()\fR functions are the same as \fBprintf()\fR, \fBfprintf()\fR,
\fBsprintf()\fR, \fBsnprintf()\fR, and \fBasprintf()\fR, respectively, except
that instead of being called with a variable number of arguments, they are
called with an argument list as defined in the \fB<stdarg.h>\fR header. See
\fBprintf\fR(3C).
.sp
.LP
The \fB<stdarg.h>\fR header defines the type \fBva_list\fR and a set of macros
for advancing through a list of arguments whose number and types may vary. The
argument \fIap\fR to the \fBvprint\fR family of functions is of type
\fBva_list\fR. This argument is used with the <\fBstdarg.h\fR> header file
macros \fBva_start()\fR, \fBva_arg()\fR, and \fBva_end()\fR (see
\fBstdarg\fR(3EXT)). The \fBEXAMPLES\fR section below demonstrates the use of
\fBva_start()\fR and \fBva_end()\fR with \fBvprintf()\fR.
.sp
.LP
The macro \fBva_alist()\fR is used as the parameter list in a function
definition, as in the function called \fBerror()\fR in the example below. The
macro \fBva_start(\fR\fIap, name\fR\fB),\fR where \fIap\fR is of type
\fBva_list\fR and \fIname\fR is the rightmost parameter (just before
\|.\|.\|.), must be called before any attempt to traverse and access unnamed
arguments is made. The  \fBva_end(\fR\fIap\fR\fB)\fR macro must be invoked when
all desired arguments have been accessed. The argument list in \fIap\fR can be
traversed again if \fBva_start()\fR is called again after \fBva_end()\fR. In
the example below, the \fBerror()\fR arguments (\fIarg1\fR, \fIarg2\fR,
\&.\|.\|.) are passed to \fBvfprintf()\fR in the argument \fIap\fR.
.SH RETURN VALUES
Refer to \fBprintf\fR(3C).
.SH ERRORS
The \fBvprintf()\fR and \fBvfprintf()\fR functions will fail if either the
\fIstream\fR is unbuffered or the \fIstream\fR's buffer needed to be flushed
and:
.sp
.ne 2
.na
\fB\fBEFBIG\fR\fR
.ad
.RS 9n
The file is a regular file and an attempt was made to write at or beyond the
offset maximum.
.RE

.SH EXAMPLES
\fBExample 1 \fRUsing \fBvprintf()\fR to write an error routine.
.sp
.LP
The following demonstrates how \fBvfprintf()\fR could be used to write an error
routine:

.sp
.in +2
.nf
#include <stdio.h>
#include <stdarg.h>
\&.\|.\|.
/*
 *   error should be called like
 *         error(function_name, format, arg1, \&.\|.\|.);
 */
void error(char *function_name, char *format, \&.\|.\|.)
{
        va_list ap;
        va_start(ap, format);
        /* print out name of function causing error */
        (void) fprintf(stderr, "ERR in %s: ", function_name);
        /* print out remainder of message */
        (void) vfprintf(stderr, format, ap);
        va_end(ap);
        (void) abort();
}
.fi
.in -2

.SH ATTRIBUTES
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Committed
_
MT-Level	See below.
_
Standard	See below.
.TE

.sp
.LP
All of these functions can be used safely in multithreaded applications, as
long as \fBsetlocale\fR(3C) is not being called to change the locale.
.sp
.LP
See \fBstandards\fR(7) for the standards conformance of \fBvprintf()\fR,
\fBvfprintf()\fR, \fBvsprintf()\fR, and \fBvsnprintf()\fR. The
\fBvasprintf()\fR function is modeled on the one that appears in the FreeBSD,
NetBSD, and GNU C libraries.
.SH SEE ALSO
.BR printf (3C),
.BR stdarg (3EXT),
.BR attributes (7),
.BR standards (7)
.SH NOTES
The \fBvsnprintf()\fR return value when \fIn\fR = 0 was changed in the Solaris
10 release. The change was based on the SUSv3 specification. The previous
behavior was based on the initial SUSv2 specification, where \fBvsnprintf()\fR
when \fIn\fR = 0 returns an unspecified value less than 1.
